runtests with output arguments

[Colin Macdonald]

Hi folks,

I'd like to improve "runtests".  I submitted some patches to add 
optional output arguments [1].  E.g.,

>> success = runtests('.')

>> [npass, total, nxfail, nskip] = runtests('.')

I also changed it so that "runtests DIR" execute tests on 'DIR/@class' 
(previous behaviour was just the m-files in DIR).  This was already the 
behaviour for runtests without arguments.

Are these welcome changes?

(I do know about "__run_test_suite__" but the underscores have always 
scared me off.)

[1] https://savannah.gnu.org/patch/?9220

cheers,
Colin